The effect of fibre fractures in the bridging zone of fatigue cracked Ti-6Al-4V/SiC fibre composites

The aim of the paper is to study the partitioning of stress between bridging and broken fibres and the nearby matrix in the region around a fatigue crack in the matrix of a Ti-6Al-4V/SCS-6 SiC fibre composite. This was achieved by using synchrotron X-ray radiation to perform a combination of high spatial resolution tomographic imaging and strain mapping. The average elastic fibre strain for each ply was mapped with distance from the crack, ply by ply. Two samples were examined; one in which there were no broken fibres and one in which some fibres in ply 1 had broken. The contributions of broken and bridging fibres were separated using a double peak fitting routine. The interfacial stress variation and the extent of interfacial debonding were deduced from the fibre strain profiles. Contrary to most micromechanical models the interfacial frictional sliding stress was not found to be constant along the fibre length, but to decrease approximately linearly towards the crack plane. Upon unloading the fibres were found to undergo reverse sliding at the interface